Multiple bitrate streaming with IBM Watson Media

When streaming to IBM Watson Media, you can send either a single bitrate or multiple bitrate streams to your IBM Watson Media channel ingest point.

What is video quality of experience (QoE)?

To engage and retain their audiences, Internet video broadcasters must deliver the best possible video Quality of Experience to their viewers. An enjoyable video viewing experience is only obtained when the sharpest possible video quality is delivered continuously to the player without experiencing playback interruptions. Studies show that despite high picture quality, viewers most typically abandon video sessions if frequent playback interruptions are experienced.

Since high video quality is achieved with a combination of higher resolutions and frame rates, encoding higher quality video (e.g. HD) yields higher bitrates, for a real-time data stream that must be delivered to the player on time. Considering that network bandwidth fluctuates during a video session, a tradeoff between video quality and smooth playback must be made. High QoE streaming is always achieved by dynamically striking a balance between these factors.

In summary, to deliver engaging video QoE, smooth streaming is as important as video quality, presenting a tradeoff that must be adjusted dynamically during a video session.

Why are multiple bitrates important?

Having a multi-bitrate representation of the video content in each video session enables the use of Adaptive Bitrate (ABR) streaming technology to dynamically address the quality tradeoff and maximize viewer’s QoE during the video session. To do that, ABR players constantly measure available network bandwidth and dynamically adjust video bitrate to match it. This is done by seamlessly switching among the video bitrates in the representation without interruptions.

The IBM Watson Media player maximizes QoE, ensuring that viewers get the maximum video quality attainable at any moment with smooth playback, avoiding pauses or re-buffering events.

The advantages of ABR in the IBM Watson Media player can be clearly visualized by analyzing the dynamics of the opposite case: a single bitrate video session. While some viewers might be on fast connections and are able to watch an HD stream, other viewers will be on slower connections and the live stream or recorded video will pause (rebuffer) frequently for them. When sending only a single bitrate stream, a solution to this is to send a medium-quality stream so that both groups of viewers can watch a stream that is of acceptable quality, but not so high as to cause buffering. The downside of this approach is that the viewers on fast connections aren't getting the best quality, and the viewers on slow connections might still experience some buffering. With multiple bitrate streaming, you don't need to make this compromise and you instead send multiple quality streams so each viewer can watch a stream optimized for their bandwidth. For example, someone on a fast internet connection can view an HD-quality stream while someone on a slower connection can view a lower quality stream without buffering, and someone with a medium-quality connection can view a medium-quality stream. QoE is therefore maximized for each viewer at any given moment.

IBM Watson Media Live Cloud Transcoding

While it is preferable to stream in multiple bitrates from the source, one challenge of multiple bitrate streaming is you need to have a powerful processor to encode multiple streams in parallel, and ample bandwidth to send multiple streams in parallel. In many situations, both the processing power available and the bandwidth available is limited, so encoding and sending multiple streams from the source of the video signal is not practical. This is why we developed the Cloud Transcoding service in IBM Watson Media. IBM Watson Media's Cloud Transcoding service provides the benefits of multiple bitrate streaming but only require a single stream ingest. You can send a single high resolution stream, but your viewers can receive multiple streams optimized for their connections.

When utilizing IBM Cloud Live Transcoding, you send a single high resolution stream that meets the required encoding specifications and it is re-encoded into following lower bitrate / resolution streams. Please see our article with encoding specifications for the required input format.

Quality

Resolution

Video Bitrate

Audio Bitrate

Audio Sample Rate

Frames Per Second

Video Codec

h.264 Profile

Keyframe interval

Audio Codec

Audio Channels

HD 1080

1920x1080

3,000 kbps

192 kbps

48 kHz

25/30/60

h.264

Main or High

1 Second

AAC-LC

Stereo

HD 720

1280x720

1,500 kbps

192 kbps

48 kHz

25/30/60

h.264

Main

1 Second

AAC-LC

Mono or Stero

480p

854x480

1,000 kbps

128 kbps

48 kHz

25/30

h.264

Main

1 Second

AAC-LC

Mono or Stereo

360p

640x360

750 kbps

128 kbps

48 kHz

25/30

h.264

Main

1 Second

AAC-LC

Mono or Stereo

240p

426x240

500 kbps

128 kbps

48 kHz

25/30

h.264

Main

1 Second

AAC-LC

Mono

64k

426x240

200 kbps

56 kbps

48 kHz

6

h.264

Main

1 Second

AAC-LC

Mono

Accessing Cloud Transcoding Settings:

log in to your account then

go to the channel settings tab for the channel you wish to enable.

Choose Broadcast settings

then Multi-quality streaming settings. You will see a list of checks that allow you to set what versions of your streams you wish to have transcoded. Options will vary according to your plan and ingest stream quality. A1080p ingest example follows:

Multiple bitrates from external encoders (local transcoding)

Some encoders will allow you to send up to 4 bitrates from your encoder and these will be passed through to the player as you send them. If you have sufficient encoder processing power and bandwidth, this can be used as an alternative to using IBM Watson Media Live Transcoding. When sending multiple bitrates to the player, the stream bitrates will display in place of the resolution when the streams share the same resolution. Please check the manual for your specific encoder to determine how this can be done. We have included two examples below: